1. Field of the Invention
The present invention generally relates to deployable structures whose shapes can be controlled and altered to modify their size, stiffness and/or damping characteristics. More particularly, this invention relates to a lightweight deployable structure that is capable of large displacements to achieve a variety of shapes with controlled precision, capable of being returned to a desired shape after being subjected to a disturbance force, and characterized by enhanced vibration isolation.
2. Description of the Prior Art
As used herein, deployable structures are generally characterized by a combination of trusses or struts that are interconnected in a manner that enables the structure to be articulated between a collapsed, retracted or stowed configuration and a deployed configuration. Such structures find uses in a wide variety of applications, including portable support structures such as platforms and bridges, vibration isolation for machinery, and structures for use in space that, because of their size, must be collapsible for transport to space. Advantages of deployable structures include improved efficiency because a deployable structure can be entirely assembled during manufacture rather than in the field, improved design performance because greater precision can typically be attained for units assembled during manufacture than for those requiring field assembly, and lower transportation costs because collapsed units are more compact for storage and shipping.
The existing technology for deployable structures is generally focused on two types of structures. A first type is the more traditional truss structure that employs heavy trusses which are mechanically interconnected with pins, welds or bolts. Because of the manner in which the trusses are secured directly together, this type of deployable structure tends to be relatively heavy for the degree of stiffness achieved, often requires powerful actuators to deploy and retract the structure, and readily transmits high frequency disturbances. Accordingly, truss structures are typically limited to applications in which weight, accuracy and vibration isolation are not paramount.
Another known type of deployable structure employs piezoelectric members to precisely control the dimension and damping of the structure. Because piezoelectric materials are brittle and therefore incapable of sustaining high loads, these deployable structures, often referred to as "smart structures," are generally limited to low load applications where minimal displacements are adequate.
A more recent deployable structure design of considerable experimental interest employs struts maintained in static equilibrium by a number of tension members, or "tendons," such that the struts do not touch each other. As discussed in the article "Double-Layer Tensegrity Grids as Deployable Structures," A. Hanaor, International Journal of Space Structures, Vol. 8, Nos. 1 & 2 (1993), such structures, referred to as "tensegrity structures," can be deployed and retracted by either elongating or shortening the struts and/or tendons. Notably, tensegrity structures are capable of larger displacements and higher loads than the above-noted "smart structures" and provide better vibration isolation as compared to the more traditional truss structures. Therefore, it would be desirable if a deployable structure characterized by the functional advantages of a tensegrity structure were available in a lightweight configuration whose shape could be precisely monitored and controlled, and whose stiffness could be modified, for use in a wide variety of applications in which weight, load capacity, accuracy and/or vibration isolation are important. In particular, it would be desirable if a tensegrity structure were available that was capable of responding to and counteracting disturbance forces in order to establish and maintain a structural or shape configuration.